Structural health monitoring (SHM) based on the propagation of guided waves has been widely applied in engineering practice to conduct on-line identification of impact or micro-scale structural damage such as fatigue cracks. To capture the guided waves, conventional metal-foil strain gauges are rarely used because of their limitation in sensing strain signals under ultra-high frequencies (for example beyond 100 kHz). Piezoelectric sensors such as those made of lead titanate zirconate (PZT), on the other hand, are most-widely used due to their high sensitivity in measuring ultrasonic strains having very low magnitudes. However, some obvious shortcomings are associated with PZT-type sensors. For example, their rigid material properties are possible to cause variations in the material and geometric properties of the host structures, and PZT sensors might be easily damaged because of their fragility. Another existing problem is that in order to obtain impact/damage information as precisely as possible, the distribution of sensors needs to be arranged in an extremely dense manner. Dense distribution of the sensors is difficult to be implemented in applications because of shortage of existing practical ways for sensor attachment, circuit construction and wire arrangement.
Flexible and lightweight nanocomposites fabricated by blending nanofillers with a polymer have been intensively investigated in recent years in capturing dynamic strain signals and in the application of SHM. For example, a sensing network comprising a plurality of nanocomposite sensing elements for SHM has been disclosed in U.S. patent application Ser. No. 15/235,113 filed on Aug. 12, 2016, the disclosure of which is incorporated by reference herein. Compared with conventional PZT sensors, a nanocomposite can be directly coated on a structure's surface to generate a sensing network with a freely-designed distribution geometry at a very high density. Since the essence of the strain sensing capacity of the nanocomposite resides on its piezoresistive nature, resistance-voltage (R-V) transformation systems are of necessity to be included to generate voltage signals based on the resistance variation of the sensors. The voltage signals are captured and further interpreted by commonly used electrical devices. For each element of the nanocomposite sensing network, an independent R-V unit (circuit) is needed, which implies that a large number of units should be integrated in a SHM system involving dense sensing networks.
Although the realization of a R-V transformation system for a nanocomposite sensing network faces many practical challenges, such challenges have not been widely addressed in the art. There is a need in the art for a design of R-V transformation system for the nanocomposite sensing network. Such design may also benefit R-V transformation for other non-nanocomposite sensing networks facing similar problems.